Activity-dependent dendrite patterning is an essential mechanism by which neurons establish their connectivity in the brain. The long-term goal of the proposed research is to investigate the role of ubiquitin signaling in the control of activity-dependent dendrite morphogenesis. We have discovered a function for a cullin-based ubiquitin ligase in the proper control of dendrite outgrowth. Knockdown of the ligase substrate- binding subunit results in the deregulated elongation of dendritic arbors. This deregulation persists under conditions of activity-deprivation that normally impede dendrite growth and promote retraction. Furthermore, neuronal activity robustly downregulates the expression of the ligase substrate-binding subunit, in a manner dependent on Ca2+ influx through voltage-gated calcium channels. These data suggest that Ca2+ signaling represses this ligase in neurons to promote dendrite growth. We will extend these analyses by conducting phenotype rescue experiments and time-lapse imaging using primary neurons, organotypic brain slices, and the in vivo cerebellar cortex of postnatal rat pups. We will apply candidate-based and unbiased biochemical approaches to identify ligase substrates that might regulate dendrite growth. We will use reporter assays, biochemical and molecular biological techniques to elucidate the mechanism by which Ca2+ signaling represses the expression of the ligase substrate-binding subunit. These studies will reveal a link between Ca2+ signaling and the regulation of ubiquitin ligases, and will advance our understanding of cell-intrinsic pathways that govern activity-dependent dendrite patterning, a major mechanism for the establishment of brain circuitry. PUBLIC HEALTH RELEVANCE: Ubiquitin ligases instruct an enormous diversity of cellular events, but their involvement in calcium-guided dendrite growth has remained unexplored. Neuronal activity-guided dendrite growth is essential to the establishment of brain circuits, and its deregulation is thought to underlie disorders like autism, mental retardation and schizophrenia. Understanding the cell-intrinsic pathways that control activity-dependent dendrite growth will better enable us to design therapeutics to treat these complex neurological disorders.